The present invention relates to a magnetic material-inverting display panel which forms a display by inverting magnetic display material with a magnet and erasing the display by inverting the materials with a magnet from the same side. More precisely, it relates to a magnetic material-inverting display panel wherein a magnetic display material having magnetic poles of opposite signs tinged with different colors by placing an opaque thin metal layer on one surface and making the color of another surface different from that of the thin metal layer of one surface.
In a prior magnetic display panel, fine particles of a magnetic material are dispersed into a dispersion. A display was formed by migrating the magnetic particles to a surface of the panel at which a magnet is operated. The display was erased through precipitation of the magnetic particles by operating a magnet from the opposite surface. This type of the magnetic display panel had a drawback that the apparatus becomes complex and large since erasure of a display should be carried out from backside of the panel. In addition, when said magnetic particles were migrated to the display panel, it was difficult to erase only unnecessary part of the display.
Furthermore, Japanese Patent Publication No. 59-32796/1984, which is incorporated herein by reference, proposes a magnetic display panel which realizes a display by inverting display magnetic particles. The panel uses a liquid dispersion dispersed with magnetic particles having a residual magnetic moment of 0.2 to 10 emu/g and a coercive force of not less than 500 oersteds, and having a yield value of not less than 5.0 N/m2.
The panel, however, had suffered from problems of a low contrast and an unclearness owing to insufficient inversion even when a display was formed by inverting magnetic particles or the display was erased.
The purpose of the present invention is to provide a magnetic material-inverting display panel which improves clearness of a display and its erasure of the panel, the display being formed by inverting magnetic display material. In particular, a liquid dispersion in a display panel has a yield value and contains a magnetic display material in fine particle form having magnetic poles of opposite signs tinged with different colors by providing an opaque thin metal layer on at least one surface and making the color of another surface different from that of the thin metal layer of the one surface, the dispersion also includes a dispersion medium and a thickener as other main components and is supported by a support. A ratio between the inner volume V of the support supporting the liquid dispersion and the volume W of the magnetic display material in fine particle form is W/Vxc3x97100=1 to 17%. Total area of S-pole-surfaces or N-pole-surfaces of the magnetic display material in fine particle form to be dispersed in a liquid dispersion of the panel is from 60% to 1500% of the display surface area of the display panel.
The magnetic display material to be used in the present invention is a magnetic material having magnetic poles of opposite signs tinged with different colors by placing an opaque thin metal layer on one surface and making the color of another surface different from that of the thin metal layer of one surface. The magnetic material is inverted by the action of magnetism to form a display. For example, when the display surface of the panel is swept with S-pole of a writing magnet, N-pole surfaces of the magnetic material is arranged at the panel surface to make it N-pole color. Upon writing the surface with N-pole of the magnetic pen, the magnetic material is inverted and S-pole surface appears to form a display of the color. When the panel is again swept with S-pole of the magnetic pen, the materials are inverted and the display disappears, whereby display having a color of the metal and a color of the magnetic material is obtained.
In the present invention, the ratio between the inner volume V of the support supporting the liquid dispersion and the volume W of the magnetic display material in fine particle form should preferably be W/Vxc3x97100=1% to 17%. When the ratio is smaller than 1%, a display tends to be unclear owing to the small amount of the display material, and, when the ratio exceeds 17%, smooth inversion tends to be difficult owing to mutual interference of the display material at the inversion. The same volume ratio is preferred in the cases where the magnetic display material is conteined in a honeycomb cell or a capsule. The ratio between the inner volume V of a unit cell or a unit capsule and the volume W of the magnetic display material therein should also preferably be W/Vxc3x97100=1% to 17%.
Furthermore, in the present invention, the total surface area of S-poles or N-poles of the magnetic display material should be from 60% to 1500% of the display surface area of the display panel for realizing a clear display.
The display surface area of the display panel means the area of the flat surface for displaying as a display panel containing a liquid dispersion in which the magnetic display material is dispersed.
The present inventors have discovered that one of the reasons of unclear display of the earlier magnetic material-inverting display panel is improperness of the surface area of S-poles or N-poles of the magnetic material for displaying relative to the display surface area of the panel. Another reason is insufficient inversion of the magnetic material.
When the surface area of S-poles or N-poles of the magnetic material for displaying is smaller than 60% of the display surface area of the panel, the displayed color tends to be pale and color difference between the displayed color and the color of the background support tends to be small, so that the contrast becomes low and the resulting display becomes unclear.
On the other hand, when the surface area exceeds 1500%, owing to too much degree of mutual interference of magnetic material, the inversion tends to be difficult to result in occurrence of an uninverted material, a material showing boundary surface between the S-pole and the N-pole, and the like, so that the resulting display has a mixed color thereof and a clear display cannot be formed.
The liquid dispersion in which the magnetic display material is dispersed must have a specific yield value and viscosity. The yield value is necessary for properly dispersing the magnetic display material in the liquid dispersion, inverting it properly by magnetism, and preventing their precipitation. The viscosity is required for inverting only the part exposed to magnetism when the display panel is exposed to magnetism. Namely, it is preferred that the liquid dispersion has a yield value of 0.15 to 7.5 N/m2 and a viscosity of 3 to 350 mPaxc2x7s. As a thickner for imparting a yield value, an inorganic substance such as AEROSIL can be used. Inorganic thickners, however, have drawbacks that the viscosity and the yield value change with a lapse of time. To the contrary, an organic thickner selected from fatty acid bisamides, hydrogenated castor oil, and amides of N-acylamino acids is preferable owing to advantages that they impart a yield value, and the viscosity and the yield value hardly change with a lapse of time.
In the case that the liquid dispersion has a yield value and a viscosity of out of the ranges of 0.15 to 7.5 N/m2 and 3 to 350 mPaxc2x7s respectively, although the yield value and the viscosity are still acceptable, stability in maintenance of the formed display tends to be deteriorated and, owing to assembly of surrounding magnetic material at writing with a magnetic pen, distribution of the magnetic material tends to be inhomogeneous, so that the color of periphery of a display formed through inversion and the color of background of the display formed by an uninverted magnetic material at the surrounding part of the display tends to change. As a result, the display tends to unclear as a whole and thus, the clearness tends to be deteriorated.
The magnetic display material to be used in the present invention has different colors at the S-pole surface and the N-pole surface. So long as an opaque thin metal layer is placed on its one surface, it is not limited to a particular form or shape. However, in view of the display-formability at writing with a magnetic pen and clearness of the display formed, it is preferred that the magnetic display material is obtained by dispersing magnetic particles into a synthetic resin and/or synthetic rubber composition having a specific color to form a magnetic layer, and cutting or pulverizing a laminate formed by placing an opaque thin metal layer at one surface of the layer or the magnetic display material is obtained by laminating a colored sheet having a different color on one surface, and cutting or pulverizing a laminate formed by placing an opaque thin metal layer on at least one surface. The color of the surface on which an opaque thin metal layer is not placed may be the color of the magnetic material itself without coloring the magnetic material layer. Also, a colored layer may be provided on both surfaces or on one surface, while the thin metal layer is provided on one surface.
Alternatively, the S-pole surface and N-pole surface are tinged with different colors, and a clear thin metal layer may be provided on both surfaces to result in a color of metallic tone.
From the present inventors"" study, the magnetic display material is inverted by the action of magnetic force of the opposite pole, and a magnetic material in a flat or foil form or shape is inverted in a stacked state with sliding each other. Accordingly, such material is preferable because not only the speed of formation of a display is high but also a clear display is formed with little coexistence of an uninverted or insufficiently inverted material.
In particular, in the case of flat or foil-shaped magnetic display material, it should be careful that, when total surface area of S-poles or N-poles of the magnetic display material is not less than 1500% of display area of the panel, inversion of the stacked material with sliding each other becomes insufficient owing to the mutual interference.
Most preferred unclear layer placed on colored surfaces of the magnetic particles is an unclear thin layer formed by metal vapor deposition.
When an unclear thin metal layer is provided on the magnetic display material, a display is formed by a combination of metallic luster and non-metallic luster, so that a high contrast and an improved clearness of the display are resulted in.
The magnetic display material tends to be charged with static electricity owing to friction between them at the inversion. Especially, the flat or foil-shaped magnetic display material is easy to be electrostatically charged since they are inverted in a stacked state with sliding each other. When the magnetic display material is electrostatically charged, the magnetic display material aggregates, so that its smooth inversion becomes difficult or some of the material is not inverted. As a result, there occurs a case that a clear display by the magnetic display material tinged with different colors cannot be attained, and therefore, the electrostatic charging is not preferred. A good display can be attained by mixing an antistatic agent into the liquid dispersion of the magnetic display material.
As the antistatic agent, one or more selected from sulfation products of polybutene, aliphatic alkyl quaternary ammonium salts, aminoethanol-epichlorohydrin polycondensates, alkylbenzenesulfonic acids, metallic salts of alkylsalicylic acids, sulfosuccinic acid salts, dialkylsulfosuccinic acid salts, and metallic salts of dodecylbenzenesulfonic acid may be used. In particular, preferred are a mixture of sulfation products of polybutene, aliphatic alkyl quaternary ammonium salts, aminoethanol-epichlorohydrin polycondensates, and alkylbenzenesulfonic acids, a mixture of chromium salts of alkylsalicylic acids, calcium salt of sulfosuccinic acid, and a polymer.
The support for supporting a liquid dispersion of magnetic display material is not particularly limited and the following are optionally used: a support composed of two substrates placed with a space between them and sealed at their periphery; a support wherein regular hexagonal honeycomb cells are placed between above two substrates; a support wherein capsules are placed at the substrate; and the like.